A conveyer apparatus, such as an escalator and a moving walkway, includes a plurality of footsteps provided with footstep rollers. Since these plural footsteps are linked to each other at predetermined pitches through an endless footstep chain, the footsteps are integrated with the footstep chain. Since the footstep chain is driven by a chain drive mechanism, all the foot steps can move synchronously without leaving any space between the footsteps. Additionally, with the engagement of the plural footstep rollers with a footstep guide rail disposed in a structure, these footsteps move between an entrance and an exit circulatively while being supported by the footstep guide rail. Note, it is generally the case that a plurality of footsteps move horizontally in the moving walkway. In this view, there is a case that the footsteps are called “footplates”. In this specification, however, the notation will be unified to “footsteps”, including the footplates in a moving walkway.
In the field of chain drive mechanism for driving a footstep chain, there is a mechanism in which a drive motor is transmitted to a footstep chain through a drive sprocket in an arrangement where a turn-over end of the footstep chain is wound around the drive sprocket rotated by driving force of the drive motor. Normally, such a chain drive mechanism is arranged in a structure called a “truss”, which is in the vicinity of entrance or exit of a conveyer apparatus.
Hitherto, it requires sufficient space to install a truss in which a chain drive mechanism. Due to progress in the installation technology etc., nowadays, the truss can be miniaturized in size. In this view, there is an attempt to minimize the size of the whole conveyer apparatus, saving an installation space of the apparatus. In the case of a small-sized truss as above, a small-diameter sprocket would be required as the drive sprocket of a chain drive mechanism. However, if such a small-diameter sprocket is employed as the drive sprocket of the chain drive mechanism, then a problem arises in that great unevenness is produced in the velocity of the footstep rollers linked by the footstep chain, being actualized in the form of vibrations of the footsteps and further deteriorating the ride quality of the conveyer apparatus.
In the technology to accomplish a smooth movement of footsteps with restriction of velocity unevenness about the footstep rollers, a technique is proposed (Japanese Patent Application Laid-open (Heisei) No. 8-217368). In the disclosed technique, for instance, the level of a horizontal surface (travelling track) of a footstep guide rail is established higher than the tangential line of a drive sprocket by an interval ho. In connection, the drive sprocket is provided, at its introductory end, with a compensating rail having a curved track. In operation, the footstep rollers are respectively engaged with the drive sprocket while being guided by the curved track of the compensating rail.
In order to accomplish a smooth movement of the footsteps with restriction of velocity unevenness of the footstep rollers, according to the art described in the Patent Document, it is performed, on a basis of a geometric model, to apply an instantaneous angle φ of a link pin (footstep roller) meshing with the drive sprocket and instantaneous angles ε1, ε2 of a link of the footstep chain to a tangential line of the drive sprocket to definitional equations, obtaining an optimal value for the above interval ho and an optimal curve of the compensating rail.
According to the art described in the above Patent Document, it is possible to suppress the velocity unevenness of the footstep rollers effectively. However, since a level of the horizontal surface of the footstep guide rail is relatively higher than the drive sprocket, the same art has a disadvantage in obtaining a minimized size of the whole conveyer apparatus. Thus, it is noted that as an interval ho between the tangential line of the drive sprocket and a horizontal surface of the footstep guide rail is proportional to a link length of the footstep chain. Therefore, if a small-diameter sprocket is used for the drive sprocket especially, the link length of the footstep chain against the drive sprocket becomes larger relatively, so that the interval ho between the tangential line of the drive sprocket and the horizontal surface of the footstep guide rail grows larger. Such an increase in the interval ho causes the truss to be large-sized, producing an obstacle in obtaining a minimized size of the whole conveyer apparatus.
Additionally, when considering a situation where the conveyer apparatus is driven while reversing outward and homeward routes, the return side of the footstep-guide rail has to be arranged below the drive sprocket by a similar interval ho, thereby requiring a considerable height of the apparatus for such upper and lower intervals (2×ho).
If the drive sprocket is formed with 348.4 mm in the pitch-circle diameter and eight teeth and the link length of the footstep chain is 133.33 mm, the interval ho between the tangential line of the drive sprocket and the horizontal surface of the footstep guide rail has to be more than 35.3 mm in order to completely eliminate the velocity unevenness of the footstep roller in the above-mentioned prior art, according to the inventors' trial calculation. Further totalizing both of the outward side and the return side of the apparatus, it is necessary for the apparatus to make sure of an extra height of 70.6 mm (2×ho) in addition to the size of the drive sprocket.
Therefore, it results in spoiling the space-saving effect that is brought by reducing the pitch-circle diameter of the drive sprocket down as far as 348.4 mm.